Plating is an important and necessary step in the high performance chip fabrication process. When plating, it is necessary to form a good ohmic contact with a seed layer on/or near a circumferential edge of a substrate. Different conventional techniques exist to accomplish this task. According to one technique, for example, a great number of contact fingers, upwards of 130, are used to form contacts with the seed layer on the circumferential edge of a wafer. The contact fingers, which are typically metallic, are coupled to the circumferential edge of the wafer in accordance with any known method.
FIG. 1A illustrates a top view of a conventional configuration showing contact fingers 12 coupled to the wafer 2 during the plating process. As illustrated, a large number of contact fingers 12 extending from a housing 11 are evenly distributed around the circumferential edge 7 of the wafer 2. The housing 11 has a ring shape corresponding to the shape of the circumferential edge 7 of the wafer 2. An electric potential (cathode) is then applied to the wires 13 or housing 11 that are further coupled to the contact fingers 12 within the housing 11. This, in turn, provides the electric potential to the circumferential edge 7 of the wafer 2, thereby allowing the wafer surface to be plated. Instead of using the contact fingers 12 as described above, the electric potential can be applied to the wafer using a ring conductor.
FIG. 1B illustrates a cross sectional view of a conventional plating apparatus as described with reference to FIG. 1A. An entire back face 6 of the wafer 2 rests against a conventional chuck 8, and a vacuum 10 is used to ensure that the wafer 2 is stationary with respect to the chuck 8 while loading and/or plating the wafer 2. Regions adjacent to the circumferential edge 7 of the front face 4 of the wafer 2 are coupled to the contact fingers 12 as described above. A plating solution, typically a metal solution, is flowed in the direction of arrow 18 to the front face 4 of the wafer 2. When an electric potential is applied between an anode electrode 19, and the circumferential edge 7 of the wafer 2, the front face 4 of the wafer can be plated with the metal species contained in the plating solution.
Contact fingers are critical components of the wafer plating process as they provide the necessary electrical potential to the wafer. However, conventional plating systems such as described above have many drawbacks and disadvantages. For example, during the plating process, metal from the plating solution may be electroplated on the contact fingers, thereby generating contaminating particles. In addition, the electroplated metal on the contact fingers increases contact resistance resulting in a high voltage drop and failure. Moreover, over time, the contact fingers are susceptible to corrosion and/or fatigue. Failure of such contact fingers then leads to non-uniform wafer plating, which may cause irreparable damage to the semiconductor wafer, thereby resulting in lost products and revenues for the manufacturer.
Thus, there remains a need for a semiconductor substrate plating method and apparatus that provides plating in a dependable and reliable manner. Accordingly, a more consistent method and apparatus for providing an electrical contact to a semiconductor substrate during plating is needed.